1. Field of the Technology
The present disclosure is directed to parts for earth-boring bits including hybrid cemented carbide composites, and also to methods of making parts for earth-boring bits including hybrid cemented carbide composites. Examples of parts for earth-boring bits included within the present disclosure include earth-boring bit bodies, roller cones, and mud nozzles.
2. Description of the Background of the Technology
Earth-boring bits used for oil and gas well drilling may have fixed or rotatable cutting elements. Fixed-cutter earth-boring bits typically include polycrystalline diamond compacts (PDCs) attached to a solid holder or bit body. Roller cone earth-boring bits typically include cemented carbide cutting inserts attached to multiple rotatable conical holders that form part of the bit. The rotatable conical holders are variously referred to in the art as “roller cones”, “insert roller cones”, or simply as “cones”. Earth-boring bits typically are secured to the terminal end of a drill string, which is rotated from the surface or by mud motors located just above the bit on the drill string. Drilling fluid or mud is pumped down the hollow drill string and “mud nozzles” formed in the bit body. The drilling fluid or mud cools and lubricates the bit as it rotates and also carries material cut by the bit to the surface.
The bit body and other parts of earth-boring bits are subjected to many forms of wear as they operate in the harsh downhole environment. A common form of wear is abrasive wear caused by contact with abrasive rock formations. In addition, the drilling mud, which is laden with rock cuttings, causes erosive wear on the bit. The service life of an earth-boring bit is a function not only of the wear properties of the cutting elements (for example, PDCs, cemented carbide cutting inserts, or milled cutting teeth), but also is a function of the wear properties of the bit body (in the case of fixed-cutter bits) or the roller cones (in the case of roller cone bits). One way to increase the service life of an earth-boring bit is to employ bit bodies or roller cones made of materials having improved combinations of strength, toughness, and abrasion/erosion (wear) resistance.
FIG. 1 depicts a conventional roller cone earth-boring bit used for oil and gas well drilling. Roller cone earth-boring bit 10 includes bit body 12 and three rotatable conical cutters or “roller cones” 14. The bit body 12 and roller cones 14 typically are made of alloy steel. Cemented carbide cutting inserts 16 are attached about the circumference of each roller cone 14. Alternatively, the roller cones 14 may include milled cutting teeth hardfaced with tungsten carbide to improve wear resistance. Rotating the drill string causes the roller cones 14 to roll along the bottom of the drill hole, and the cutting inserts 16 sequentially contact and crush the rock in the bottom of the hole. High velocity jets of fluid pumped through fluid holes or “mud nozzles” 18 sweep the crushed rock from the bottom region and up through the drill hole. The cutting inserts 16 or teeth typically mesh to some degree as the roller cones 14 rotate, and this meshing action assists in cleaning rock from the face of the bit body 12. Attachment region 19 may be threaded and/or include other features adapted to allow the bit 10 to be connected to an end of a drill string.
FIG. 2 depicts a conventional fixed-cutter earth-boring bit body. The bit body 20 is typically made of alloy steel. According to one recent development, if a higher degree of wear and erosion resistance is desired, the bit body 20 may be formed from a cast metal-matrix composite. The composite may include, for example, carbides of tungsten bound together by a matrix of bronze, brass, or another suitable alloy characterized by a relatively low melting point. Several PDC cutters (not shown) are secured to the bit body in pockets 28, which are positioned at predetermined positions to optimize cutting performance. The bit body 20 is secured to a steel shank (not shown) that typically includes a threaded pin connection by which the bit is secured to a drive shaft of a downhole motor or a drill collar at the distal end of a drill string.
Steel bodied bits are typically machined from round stock to a desired shape, with topographical and internal features. Hard-facing techniques may be used to apply wear-resistant materials to the face of the bit body and other critical areas of the surface of the bit body.
In the conventional method for manufacturing a bit body from hard particles and a binder, a mold is milled or machined to define the exterior surface features of the bit body. Additional hand milling or clay work may also be required to create or refine topographical features of the bit body. Once the mold is complete, a preformed bit blank of steel may be disposed within the mold cavity to internally reinforce the bit body and provide a pin attachment matrix upon fabrication. Other sand, graphite, or transition or refractory metal-based inserts, such as those defining internal fluid courses, pockets for cutting elements, ridges, lands, nozzle displacements, junk slots, and/or other internal or topographical features of the bit body, may also be inserted into the cavity of the mold. Any inserts used must be placed at precise locations to ensure proper positioning of cutting elements, nozzles, junk slots, etc., in the final bit. The desired hard particles may then be placed within the mold and packed to the desired density. The hard particles are then infiltrated with a molten binder, which freezes to form a solid bit body including a discontinuous phase of hard particles embedded within a continuous phase of binder.
Recently, it has been discovered that fixed-cutter bit bodies may be fabricated from cemented carbides employing standard powder metallurgy practices (powder consolidation, followed by shaping or machining the green or presintered powder compact, and high temperature sintering). Co-pending U.S. patent application Ser. Nos. 10/848,437 and 11/116,752 disclose the use of cemented carbide composites in bit bodies for earth-boring bits, and each such application is hereby incorporated herein by reference in its entirety.
In general, cemented carbide based bit bodies provide substantial advantages over the bit bodies of the prior art, which typically are machined from steel or infiltrated carbides, since cemented carbides offer vastly superior combinations of strength, toughness, and abrasion/erosion resistance compared to steels or infiltrated carbides with copper based binders.
Referring again to FIG. 2, a typical solid, one-piece, cemented carbide bit body 20 is depicted that can be employed to make a PDC-based earth-boring bit. As can be observed, the bit body 20 essentially consists of a central portion 22 having holes 24 through which mud may be pumped, as well as arms or blades 26 having pockets 28 into which the PDC cutters are attached. The bit body 20 of FIG. 2 may be prepared by powder metal technologies. Typically, to prepare such a bit body, a mold is filled with powders that include both the binder metal and the carbide. The mold is then compacted to densify the powders and form a green compact. Due to the strength and hardness of sintered cemented carbides, the bit body is usually machined in the green compact form. The green compact may be machined to include any features desired in the final bit body. The green compact may then be sintered to achieve full or near-full density
While bit bodies and holders fabricated with cemented carbide may exhibit an increased service life compared with bit bodies and holders fabricated from conventional materials, limitations remain in using cemented carbides in these applications. The grades of cemented carbide that would be suitable for use in bit bodies and holders is limited. High toughness levels are needed to withstand the high impact forces encountered during earth-boring operations but, in general, higher toughness grades are characterized by low hardness and poor wear resistance. The cemented carbide grades commonly selected for use in bit bodies and holders, therefore, typically include relatively high binder contents, such as 20 weight percent or greater, and coarse hard particle grain sizes, having an average grain size of at least 4-5 microns. Such grades typically exhibit relatively limited wear and erosion resistance levels. Therefore, although the service lives of bit bodies and holders based on such cemented carbide grades typically exceed those of brass, bronze, and steel based bodies and holders, the increase in service life has been limited by the properties of the cemented carbide grades suitable for earth-boring applications.
Accordingly, there continues to be a need for bit bodies, roller cones, mud nozzles, and other parts for earth-boring bits having an advantageous combination of wear resistance, strength, and toughness.